1. Field of Invention
This application is a continuous-in-part application of now abandoned application Ser. No. 486.240.
The present invention relates in general to a method and apparatus for detecting a magnetic field using an anomalously strong magnetic birefringence of a magnetic fluid, and more particularly to a magnetic field sensor, a transformer, an apparatus for controlling a light intensity containing an optical shutter and an optical modulator, an optically bistable apparatus, a memory means for an optical computer and a light intensity stabilizer for lasers and an optical amplifier.
2. Brief Description of Magnetic Fluids
A magnetic fluid is a colloidal suspension containing fine ferrous colloidal particles and shows a strong magneto-optical effect in a presence of a magnetic field when it is made into a thin film. This effect was recently discovered by the inventor of this invention (see S. Taketomi; Japanese Journal of Applied Physics Vol. 22 (1983) p. 1137. Therefore, before the discovery of this effect, the main application of the magnetic fluid has been limited only for rotating shaft and exclusion seals.
The magnetic fluids consist of ferro- or ferrimagnetic colloidal particles the sizes of which are less than 200.ANG., surfactants and solvents (see R.E. Rosensweig: International Science and Technology, July 1966, page 48). When the ferro- or ferrimagnetic substances become such fine particles, each particle becomes magnetically a single magnetic domain and it possesses the property of a permanent magnet. The magnetic force originated from the permanent magnetization makes the particles coagulate and deposit. Therefore, the ferrous colloidal solution was a very unstable solution or a very dilute one to avoid coalescence of the particles before the invention of the magnetic fluid.
The magnetic fluid was invented by Pappel in 1965 (see S. S. Papell: U.S. Pat. 3,215,572 (1965)). Since the ferrous colloidal particles 1 in the magnetic field are clad with surfactant 2, they do not coalesce with each other (see FIG. 1). This method makes it possible to produce a stable colloidal solution of the ferrous colloidal particles having a high concentration.
The magnetic fluids possess strong magnetization though they are liquid. Using this property, they have been applied to rotating shaft seals (see R. E. Rosensweig et al.: Machine Design, Mar. 28, 1968. p. 145). FIG. 2 shows the principle of the magnetic fluid shaft seals. A rotating shaft 4 and stationary pole-blocks 5 are made of magnetic substances. A permanent magnet 6 is sandwiched by the two pole-blocks 5. Therefore, a magnetic circuit 7 is made between the rotating shaft 4 and the stationary part 5. A magnetic fluid 8 is strongly attracted in the gap between the rotating shaft 4 and the stationary part 5. Consequently the magnetic fluid 8 fills the gap like a O-ring of a mechanical element and works as a shaft seal. The airtight ability of the seal is excellent in comparison with any other kinds of rotating shaft seals. Therefore, the magnetic fluid seals are successfully used as vacuum shaft seals.
Many other applications of the magnetic fluid have been proposed, for example a sink float separation apparatus, a heat engine, etc (see R. E. Rosensweig: International Science and Technology, July 1966, page 48). None of the applications of the Magnetic Fluid Thin Film's Anomalous Pseudo-Cotton-Mouton effect (i.e. "MFTFAPCM" effect), however, have been proposed.